A conventional image forming apparatus of the electrophotographic type has been widely used as a copying machine, a printer, a plotter, a facsimile machine, a multi-function machine having a plurality of functions of these machines, and the like. In the image forming apparatus of this type, toner charged in a developing device is brought near to a photosensitive drum which is an example of an image bearing member and is electrostatically deposited on an electrostatic latent image on the photosensitive drum, and thus development is carried out, so that an image is formed. In order to develop the electrostatic latent image, the developing device is incorporated in the image forming apparatus. In the developing device, at a position of a developer container (developing container) opposing the photosensitive drum, a developing sleeve as a developer carrying member is rotatably provided. The developing sleeve incorporates a magnet roller as a magnetic flux generating means. As a developer, a two-component developer containing non-magnetic toner and a magnetic carrier is used.
For development, the developer is partly regulated by a developer regulating member through rotation of the developing sleeve and passes through between the developing sleeve and the developer regulating member, so that the developer is coated in a thin layer on a developing sleeve surface and then is fed to a developing region opposing the photosensitive drum. In the developing region, the developer forms a chain-like magnetic chain by a magnetic flux generated by the magnet roller. This magnetic chain is in proximity to or in contact with the photosensitive drum, and only the toner is transferred onto the electrostatic latent image formed on the surface of the photosensitive drum by a developing bias applied to the developing sleeve, so that a toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum.
Here, an amount of the developer supplied to a developing nip which is the developing region between the developing sleeve and the photosensitive drum is determined by a gap (interval) between the developing sleeve surface and the developer regulating member (hereinafter referred to as an SB gap).
Conventionally, as the developer regulating member constituting the SB gap by a simple constitution, a developer regulating member which has a cylindrical shape and which has a magnetic property has been developed (Japanese Laid-Open Patent Application (JP-A) 2008-275719). In the developing device including this developer regulating member, the magnet roller has a plurality of magnetic poles containing a developing (magnetic) pole opposing the photosensitive drum and a regulating magnetic pole opposing the developer regulating member. This magnet roller is magnetized so as to have a single (one) maximum value in a magnetic flux density distribution of the regulating magnetic pole.
In general, an application amount of the developer coated in the thin layer on the developing sleeve is controlled (managed) by M/S which is a developer weight per unit area. In the developing device including this developer regulating member, during assembling, a position of the maximum value in the magnetic flux density distribution of the regulating magnetic pole is appropriately adjusted and set at a side upstream or downstream of the SB gap, so that stabilization of M/S is realized.